Field
The present application relates to lighting technology. More specifically, the present application is directed to a light-emitting diode (LED) lamp (e.g., lighting fixture) with improved light efficacy (efficiency).
Brief Discussion of Related Art
Light sources, such as light-emitting diodes (LEDs), are a highly-attractive alternative for various lighting applications. In contrast to conventional light sources, LEDs enjoy a relatively long life span, high light output and low power consumption. In recent years, various LED lamps, which include one or more LEDs, have been designed and implemented for indoor, as well as outdoor applications.
LEDs can vary in operational characteristics for different lighting applications from minimal (e.g., about 3 lumens per watt (lm/W)) up to maximal (e.g., about 200 lm/W) operational characteristics. These operational characteristics have undergone significant changes in recent years, and will likely continue to improve.
For applications that require a large amount of light, such as outside lamps (e.g., streetlights) and other similar applications, a multiplicity of LEDs is often used (e.g., 30 LEDs-48 LEDs, or more). With higher wattage, LEDs experience limits to light output and suffer from rising heat. Accordingly, heat dissipation has been an ongoing concern for such applications.
In various applications, LEDs are generally disposed inside a housing, and the light emitted from the LEDs is generally transmitted through various optically-transparent media (e.g., plastic, silicone, glass, air, and/or others) in order to exit the housing. For visible light, most transparent media generally have refractive indices between about 1 and about 2, e.g., air having a refractive index of about 1, and glass has a refractive index of about 1.4 to about 1.6.
Light rays generally refract at the interface of media having different refractive indices. Light rays can also be reflected (e.g., internal reflection) to varying degrees at the interface based on their angle of incidence (e.g., complete reflection occurring at an incidence angle that is greater than a critical angle based on a refractive index of the particular medium). Accordingly, some light rays emitted from the multiplicity of LEDs can reflect from one or more media to the inside of the housing, limiting the overall light efficacy of the LED lamp.
Conventional reflectors, especially those having a parabolic shape, have been used in various lighting applications to focus light emitted from the light sources. Specifically, a light source is disposed at the focus of the reflector. Direct light rays (not reflected from the surface of the reflector) produce a conical beam with respect to the axis of the reflector, while the reflected light rays (i.e., reflected from the surface of the reflector) form a collimated beam in which light rays are parallel to the axis of the reflector.
While focusing the reflected light rays can minimize the potential reflection of these light rays to the inside of the housing, conventional reflectors cannot focus the direct light rays in the conical beam that are at an angle with respect to the axis of the reflector. Some of these rays, especially those toward the periphery of the light cone (peripheral light rays), can reflect from one or more media to the inside of the housing, limiting the overall light efficacy of the LED lamp.
Russian Federation Patent No. 94310 describes a “light-emitting diode lamp.” This lamp includes a metal base and light-diode modules attached to it. Each module is a thin-walled composite substrate on which LEDs are disposed, each of which has a protective outer layer executed in the form of a translucent shell made of a polymeric, translucent material possessing high mechanical strength, made, for example, from a polycarbonate plastic, and a protective inner layer executed of a cured, translucent polymeric substance, which is a translucent compound, a luminophoric material, a polymerized, translucent resin, or mixtures thereof. The combination of the protective outer layer in the form of a translucent shell and the protective inner layer formed by a cured, translucent polymeric substance, forms a first optical system for each LED with predetermined optical characteristics, such as, for example, the angle of dispersion and the transmission coefficient.
Moreover, Russian Federation Patent No. 100179 describes a “light-emitting diode lamp for areal illumination.” This lamp includes a body with a circuit board attached to it, on which there are disposed light-emitting diodes of a first optical system, each of which has a second optical system, as well as a protective screen executed of an optically-transparent material.
These known LED lamps do not have a high optical coefficient of efficiency (e.g., improved overall light efficacy or efficiency) because of high reflective losses and also because of failure to refract peripheral light rays.
It is therefore desirable to provide an LED lamp that mitigates the reflective losses of light rays and provides for refraction of peripheral light rays to improve the overall light efficacy of the LED lamp.